Well that doesn't sound good. But it's not very much evidence that something's happened - she can feel herself making up possible stories about what could have happened, but they all feel stupid, making extra connections between things that don't deserve to be glued together. He's probably fine.
...he almost always comes to the temple, though. And she doesn't think he's entirely skipped a day since she started practicing without noting beforehand that he was going to do that.
It is possible that Élie tried to help an old friend - an old enemy? - and in doing so attracted the attention of whatever Chelish forces were after the friend. It is possible that the old friend is more an enemy than he claims. And it is possible that the letter is unrelated, but that someone has connected him to the disappearance of the Chelish ambassador to Thuvia, and in that case - none of these is very likely, perhaps, but they might be too likely to ignore - she would feel awful if something had happened and she ignored it, especially with the rest of the party dispersed on their own errands like they are now -
She bites her lip and glances out at the sun. It's low. She has enough time to make it to her own house. She does not think she has enough time to make it much of anywhere else. But if something has happened, and she leaves it for an entire night - if he's dead, and someone plans to go to an effort to spoil the body, or captured, and being read or tortured for information about who he was working with - this is her imagining far worse than whatever's really happening, almost certainly, but the general point holds. If something really has happened to him then it might not be safe to leave the situation all night.
She can hear Tariq in her head, noting that she seemed chaotic now. She'd argued with him. She hadn't argued very insistently. She's not chaotic, not yet, she knows what her alignment is, but she doesn't think there's anything in particular stopping her from ending up there. As she rifles through Élie's closet and changes into ill-fitting men's clothes, she silently grants her late husband the point. She stuffs her own clothes and the letter in her pack, and then walks out of the room, trying very very hard not to call attention to herself. No one stops her. She's not sure whether that's because they haven't happened to look very closely.
She arrives at the Temple of the All-Seeing Eye just as the sun is sinking out of view. There are still wizards around; mid-circle wizards keep long hours. She asks around about whether there's a scrying mirror that someone might let her use for an hour, for a fee. She hopes her voice isn't too obviously feminine, and also hopes that no one thinks about how weird it is for a man young enough to have her voice to also be powerful enough to cast fourth-circle spells. They do, in fact, have a mirror that isn't in use, so she pays the temple staff and then tries very hard to calm herself down enough to complete the casting of the spell.
(Élie has a good will save. It might not work. But it seems like the thing to try, if she isn't very sure what sort of thing might have gone wrong.)